桂西北喀斯特土壤对生态系统退化的响应

Responses of soil properties to ecosystem degradation in Karst region of northwest Guangxi,China

在桂西北喀斯特地区选取玉米-红薯轮作地(KMS)、放牧+冬季火烧草地(KGB)、自然恢复地(KNR)和原生林地(KPF)4种典型生态系统,研究了土壤有机碳、全氮、全磷,微生物生物量碳、氮、磷和土壤结构对生态系统退化的响应.结果表明:KPF土壤有机碳、全氮、全磷和微生物生物量碳、氮、磷均极显著高于其他3种土壤;其他3种土壤中,有机碳和全氮为:KNR>KGB>KMS,但差异不显著;KMS土壤全磷含量(0.87g·kg-1)分别是KNR和KGB的2.07和9.67倍(P<0.01);KGB和KNR土壤微生物生物量碳、氮、磷含量均显著大于KMS;KGB中微生物生物量碳显著大于KNR,但二者间微生物生物量氮和磷含量差异不显著.说明减少人为干扰后喀斯特退化生态系统可以缓慢增加土壤有机碳含量,适当放牧和自然恢复都可以作为退化生态系统恢复的方式;土壤微生物生物量对生态系统的变化响应较灵敏,可以作为喀斯特地区土壤养分变化或生态系统退化的一个敏感指标.土壤结构以>0.25mm水稳性大团聚体为主(>70%)(KMS除外,以2～0.25mm团聚体为主),并以>2mm团聚体为主;土壤结构破坏率KMS(51.62%)大于KGB(23.48%),KNR和KPF较小(分别为9.09%和9.46%).说明人为干扰或农业耕作破坏了土壤水稳性大团聚体,使其向小粒级转变,土壤结构破坏率增大.对喀斯特地区退化严重的生态系统应减少人为干扰,以自然恢复等保护性措施为主.

Four typical ecosystems,i.e.,maize-sweet potato rotational cultivated land （KMS）,grazing grassland burned annually in winter （KGB）,natural restoration land （KNR）,and primary forest land （KPF）,in Karst region of northwest Guangxi were selected to investigate the responses of soil nutrients （C,N and P）,soil microbial biomass,and soil structure to the degradation of ecosystem. The contents of soil organic C,total N and P,and soil microbial biomass C,N,and P were significantly higher in KPF than in KMS,KGB,and KNR （P0.01）. In the latter three degraded ecosystems,the contents of soil organic C and total N were in the sequence of KNRKGBKMS but the difference was not significant,soil total P content in KMS （0.87 g·kg-1） was 2.07 and 9.67 times of that in KNR and KGB,respectively （P0.01）,and soil microbial biomass C,N and P contents were significantly higher in KGB and KNR than in KMS （P0.05）. The soil microbial biomass C was significantly higher in KGB than in KNR （P0.05）,but there were no significant differences in soil microbial biomass N and P between the two ecosystems. These results illustrated that the reduction of human activity could induce a slight increase of soil organic C in Karst degraded ecosystems,and proper grazing and natural restoration could be the feasible modes for the restoration of degraded ecosystem. Soil microbial biomass was more sensitive in response to the change of ecosystem,being able to be used as a sensitive indicator to reflect the change of degraded ecosystem in Karst region. In KPF,KNR,and KGB,soil water-stable macro-aggregates （0.25 mm） accounted for more than 70%,and dominated by 2 mm aggregates; while in KMS,soil water-stable macro-aggregates only occupied 40.34%,and dominated by 2-0.25 mm aggregates. The destruction rate of soil structure in KMS,KGB,KNR,and KPF was 51.62%,23.48%,9.09%,and 9.46%,respectively （P0.05）,indicating that human disturbance or farming practice destroyed soil macro-aggregates,and made the destruction rate of soil structure increased. To reduce human disturbance and implement natural rehabilitation would be the suitable ecological restoration strategy in Karst region.